Conventional clothes dryers heat a large volume of air that then passes over tumbling clothes. Water is extracted from the wet clothes by evaporation into the heated air. This conventional drying process is extremely inefficient, as at least 50% of the energy consumed by the machine goes out the vent.
The stated above inefficiency of conventional drying process is due to the fact that air is a very poor heat conductor. Thus, for example, only very small engines can be air cooled efficiently. On the other hand, some large engines, for example, an automobile engine, or a high power motorcycle engine, use water cooling because water is much better heat conductor than air.